1. Field of the Invention
The present invention relates to a magnetic tape recording apparatus and method, a magnetic tape playback apparatus and method, a format for a magnetic tape, and a storage medium product. More particularly, the present invention relates to a magnetic tape recording apparatus and method, a magnetic tape playback apparatus and method, a format for a magnetic tape, and a storage medium product, which enable high-definition video data to be recorded on or played back from the magnetic tape.
2. Description of the Related Art
Recently, with the progress of compression technology, video data, etc. have also been compressed by the DV (Digital Video) technique, for example, and recorded on a magnetic tape. A format for such compression of video data, etc. is specified as a DV format for consumer-oriented digital video cassette recorders.
FIG. 1 illustrates a construction of one track in a conventional DV format. In the DV format, video data is recorded after being subjected to the 24-25 conversion. The number of bits denoted by each numeral in FIG. 1 represents a value after being subjected to the 24-25 conversion.
A region corresponding to a contact angle of 174 degrees of a magnetic tape around a rotary magnetic head provides an effective region of one track. Outside the region of one track, an overwrite margin with a length of 1250 bits is formed. The overwrite margin serves to prevent data from remaining after being erased.
When the rotary head is rotated in sync with frequency of 60×1000/1001 Hz, the region of one track has a length of 134975 bits, and when the rotary head is rotated in sync with frequency of 60 Hz, it has a length of 134850 bits.
An ITI (Insert and Track Information) sector, an audio sector, a video sector, and a subcode sector are arranged in one track successively in the trace direction of the rotary head (i.e., in the direction from left toward right in FIG. 1). A gap G1 is formed between the ITI sector and the audio sector, a gap G2 is formed between the audio sector and the video sector, and a gap G3 is formed between the video sector and the subcode sector.
The ITI sector has a length of 3600 bits, and a preamble of 1400 bits is arranged at the head of the ITI sector to produce a clock. Subsequent to the ITI sector, an SSA (Start Sync Area) and a TIA (Track Information Area) are arranged in length of 1920 bits in this order. A bit train (sync number) necessary for detecting the position of the TIA is arranged in the SSA. Information indicating that video data is in the DV format for consumer-oriented equipment, information indicating whether the mode is an SP or LP mode, information indicating a pattern of a pilot signal of one frame, etc. are recorded in the TIA. Subsequent to the TIA, a postamble of 280 bits is arranged.
The gap G1 has a length of 625 bits.
The audio sector has a length of 11550 bits. At the head and end of the audio sector, 400 bits and 500 bits are used for a preamble and a postamble, respectively, and 10650 bits between the preamble and the postamble are used for data (audio data).
The gap G2 has a length of 700 bits.
The video sector has a length of 113225 bits. At the head and end of the video sector, 400 bits and 925 bits are used for a preamble and a postamble, respectively, and 111900 bits between the preamble and the postamble are used for data (video data).
The gap G3 has a length of 1550 bits.
The subcode sector has a length of 3725 bits when the rotary head is rotated at frequency of 60×1000/1001 Hz, and has a length of 3600 bits when the rotary head is rotated at frequency of 60 Hz. At the head and end of the subcode sector, 1200 bits are used for a preamble and 1325 bits (when the rotary head is rotated at frequency of 60×1000/1001 Hz) or 1200 bits (when the rotary head is rotated at frequency of 60 Hz) are used for a postamble, respectively, and 1200 bits between the preamble and the postamble are used for data (subcode).
In the conventional DV format, as described above, not only the gaps G1 to G3 are formed between adjacent two of the ITI sector, audio sector, video sector and the subcode sector, but also the preamble and the postamble are provided for each sector. Therefore, the conventional DV format has a drawback that it includes a relatively large amount of so-called overhead and hence cannot provide a sufficiently high level of recording rate for effective data.
Such a drawback leads to a problem as follows. When recording high-definition video data (hereinafter referred to as HD video data), for example, a bit rate of about 25 Mbps is required. However, a bit rate obtained in the conventional DV format by MP@HL in accordance with MPEG (Moving Picture Expert Group) is about 22 Mbps at maximum except for search video data. As a result, although the conventional DV format can record standard-definition video data (hereinafter referred to as SD video data), but it cannot ensure a satisfactory level of image quality when the HD video data is compressed and recorded by MP@HL or MP@H-14.